Depressive Rumination And The Default-Mode Network

People suffering from depression frequently find themselves preoccupied with shameful, guilty, or self-defeating thoughts for large parts of their day. Not only these thoughts distract from other activities, but also may prevent the resolution of the underlying life issues. The ideas that receive focused attention in these depressive ruminations are also quite distorted and often lead to more distress.

Because the way that depressed people repetitively attend to these negative thoughts in an unproductive manner calls to mind the repetitive chewing of cud by ruminants like cows or goats, psychologists use the term ruminations.

The tendency towards rumination in depression has been well documented. However, a new study by Dr. J. Paul Hamilton at the Laureate Institute for Brain Research and his colleagues at Stanford University sheds light on the brain mechanisms giving rise to these symptoms.

Brain Region Interplay

The work, by Dr. J. Paul Hamilton at the Laureate Institute for Brain Research and his colleagues at Stanford University, highlights the interplay of a brain region implicated in depression, the subgenual prefrontal cortex (sgPFC) and a brain network involved in reflection, sometimes called the default mode network (DMN).

The default mode network becomes activated when the brain’s task-oriented circuits are not engaged, for example, during times of self-referential thought.

Through a re-analysis of existing studies, the researchers show that depressive ruminations are more likely to emerge in depression when the firing of the sgPFC, signaling depressed mood, is more highly synchronized with the firing of the DMN.

The Subgenual Prefrontal Cortex and The Default Mode Network

They propose that the observed increased connectivity reflects a functional integration of sgPFC and DMN processes which, in turn, support rumination in depression.

Commented Dr. John Krystal, Editor of Biological Psychiatry:

“This study shows that depression distorts a natural process. It would seem that normally the subgenual prefrontal cortex helps to bias the reflective process supported by the default mode network so that we can consider important problems in the service of developing strategies for solving them.

However, in depression it seems that the subgenual prefrontal cortex runs amok hijacking normal self-reflection in a maladaptive way. This may be one reason that electrical stimulation of the sgPFC is helpful for some patients with severe or treatment-resistant symptoms of depression.”